Remove config_models & use external config_models repo instead.

common/djangoapps/config_models/README.rst

common/djangoapps/config_models/__init__.py

common/djangoapps/config_models/admin.py

common/djangoapps/config_models/decorators.py

common/djangoapps/config_models/management/__init__.py

.../djangoapps/config_models/management/commands/__init__.py

...oapps/config_models/management/commands/populate_model.py

common/djangoapps/config_models/models.py

common/djangoapps/config_models/templatetags.py

common/djangoapps/config_models/tests/__init__.py

common/djangoapps/config_models/tests/data/data.json

...ngoapps/config_models/tests/test_model_deserialization.py

common/djangoapps/config_models/tests/tests.py

common/djangoapps/config_models/utils.py

common/djangoapps/config_models/views.py

requirements/edx/github.txt